Method of making a target

ABSTRACT

Described is a titanium sputtering target to provide improved step coverage and a method of making same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.08/893,892, filed Jul. 11, 1997.

BACKGROUND OF THE INVENTION

As computer chips become “faster” and more capable, there is acorresponding increased demand for improved materials and methods ofmanufacturing. Although computer chips, i.e. semi-conductor devices, aremanufactured by many techniques, a typical important step in themanufacture is the deposition of thin films on a substrate. The presentinvention focuses on physical vapor deposition, PVD, wherein a mass ofmetal, i.e. “a target”, is shaped such that when a plasma is excited ina rarefied atmosphere, such as argon, at a very low pressure, the highspeed atoms of argon dislodge metal atoms from the target. Atoms fromthe target thus freed, deposit a thin film on a substrate or wafer, e.g.a single crystal of silicon, located near the target. Following a numberof various operations and additional film depositions, the wafer is madeready for dicing into individual chips. A few to several dozen chips maybe obtained from an individual wafer. The resulting chips providevarious functions in a typical computer, for example, memory, logic andapplication specific tasks, etc.

Articles embodying the chips are often made by designs that includetrenches, contact holes and via holes (also referred to as “vias”) invery small diameters. It is important that the film coverage of thebottom of the contact holes, vias, and trenches, referred to as “stepcoverage”, be maintained to a useful degree so that smaller diameters ofsuch holes can be used as higher aspect ratios are desired inapplications where electrical connection between layers is required. Thepresent invention provides a titanium sputtering target which enablesimproved step coverage.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a titaniumsputtering target that has particular texture with high fractions of<20-23> and <11-20> orientations perpendicular to target plane. Thetexture may be defined by intensities for various crystal planes thatare parallel to the target plane. A value of intensity for a crystalplane in a textured target is expressed as multiples of the intensityfor the same crystal planes in a Ti sample with a random grainorientation distribution. Intensities of crystal planes are obtainedfrom orientation distribution function based on four measured polefigures from X-ray diffraction.

In addition, the invention concerns a method of providing a titaniumsputtering target with particular desired orientation and texture, andtitanium sputtering targets that are especially useful in physical vapordeposition processes to improve step coverage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of crystal structure and orientations of Ti;

FIGS. 2A and 2B are diagrams showing a sputtering target and collimatorto attempt to improve step coverage, with an inset that explains “stepcoverage”;

FIG. 3 is a diagram that illustrates improvement in step coverage orcollimation yield by using a target with higher proportion ofperpendicular emission;

FIG. 4 Illustrates the (0002)-α texture;

FIG. 5 illustrates definition for Euler angles;

FIG. 6A is an illustration of the (20-25) texture;

FIG. 6B is an illustration of the ( 11-20) texture;

FIG. 7 is a diagram showing the relationship of (10-12), (10-13), and(20-25) planes;

FIG. 8A is an illustration of grains with twins. The area marked “a” isa twin of “b” and vise versa because they have twin orientationrelationships;

FIG. 8B is an illustration of grains that are recrystallized;

FIG. 9A is a photomicrograph of a target surface showing microstructurewith twins;

FIG. 9B is a photomicrograph of a target surface showing microstructurewith recrystallized grains;

FIG. 10 is a flow chart showing conventional target manufacturingprocess;

FIG. 11 is a flow chart illustrating an example of how a sputteringtarget may be made in accordance with the invention;

DETAILED DESCRIPTION OF THE INVENTION

An important aspect of chip manufacture is the purity of the material. Amethod and apparatus for producing very high purity titanium, and highpurity titanium so produced, are disclosed in copending applicationfiled Apr. 30, 1997 in the name of Harry Rosenberg, Nigel Winters andYun Xu, entitled Method and Apparatus for Producing Titanium Crystal andTitanium, application Ser. No. 08/846,289, now abandoned, the disclosureof said application is hereby expressly incorporated herein byreference.

Conductivity and chip speed of semi-conductor devices, using titaniumdepend on titanium purity, especially the oxygen content. Otherimportant impurities to minimize or exclude include: radioactiveelements (alpha emission can cause a memory element to change state),transition metals, e.g. Fe, Cr, Ni, (lowering amounts of these improveetching and element registry) and alkali metals, e.g. Na and K, that canmigrate to transistor elements and disrupt their function. Thus titaniumtargets must be as pure as possible in both metallic and gaseouselements for maximum usefulness and advantageously should have nodefects such as oxide or nitride inclusions. However, texture of thesputtering target is important to establish the direction of atomemission from the target and is dependent on crystallographicorientations. FIG. 1 illustrates the crystal structure and orientationof alpha phase titanium.

As the quality of semi-conductor devices improve, smaller line geometryand higher aspect ratio contact and via holes are required in chipmanufacture. In order to deposit thin, uniform films in contact and viaholes with high aspect ratio, it is necessary to direct the flux ofatoms being ejected from the target as perpendicular to the wafer aspossible. Ideally, the deposited film thickness would be the same on thewafer surface as it is at the bottom of a via or a contact hole. Theratio of these thicknesses is often referred to as “step coverage” whichis explained in the inset in FIG. 2.

The vast majority of atoms strike the wafer at various and lower angles,thereby coating the surface and sidewalls of the via or the contacthole. In this case, the film on the surface and sidewalls may become sothick as to close off the via or the contact hole, preventing properfilm thickness from being obtained at the bottom of the via or thecontact hole. However, by collimator as shown in FIG. 2 the atoms can bebetter directed to the wafer but the yield is reduced because ofdeposition on the collimator. Current sputtering target designs havetextures that result in a much wider flux distribution, yielding only asmall population of atoms that are collimated enough to be deposited inthe bottom of a via or a contact hole.

Although mechanical collimators are somewhat effective in improving stepcoverage, they present several difficulties in their use. The sputteryield is significantly reduced due to coating of the collimator becauseonly those Ti particles that travel in directions approximatelyperpendicular to the wafer surface are allowed to reach the wafer duringthe collimated sputtering. Usually, the collimator becomes so heavilycoated that it must be removed and replaced with a new one at least onceduring the targets life. Replacing the collimator results in costlydowntime.

The emission direction of sputtered atoms is preferably along certaincrystallographic orientations from a target. Therefore one effective wayto increase collimation yield (efficiency) or step coverage is to tailorthe crystal orientation distribution, i.e. crystallographic texture, ofpolycrystalline target so that a higher proportion of the atoms isemitted in a direction perpendicular to the wafer surface. Since atomsemit preferably along certain crystallographic directions, sputteringperformance such as step coverage and collimation yield (efficiency), isdependent on crystallographic texture in the targets. Textures in Titargets are mainly determined by initial texture prior to processing,metal working, and annealing conditions for high purity Ti.

FIG. 3 illustrates that a target with properly designed texture may beused with a mechanical collimator to achieve collimation of the atomflux. The collimator may be made of titanium in a honeycombconfiguration, with dimensions designed for the level of step coveragedesired.

Alpha titanium has a hexagonal close packed crystal structure attemperatures below about 880° C. with crystal orientations shown inFIG. 1. A Ti target produced by cold rolling or forging over 50%deformation followed by annealing for recrystallization has a texture of(0002)-α (typically α=20°-34°), where α is the angle between (0002)crystal plane and the target plane (FIG. 4). The angle α is dependent oninitial texture, metal working method, amount of deformation,temperature during the deformation, and heat treatment. A texture with(10-13) or (10-15) as the strongest component is often obtained aftercold rolling followed by recrystallization. The notation “( )” enclosethe Miller Bravais indices for atomic planes in hexagonal materials.

Sputtered atoms preferentially emit along near-neighbor directions. Inthis description “> ≦” encloses (identifies) Miller Bravais indices fordirection in a hexagonal crystal. The direction of nearest neighbor forTi is <20-23 > which is the direction from an atom in one close-packedcrystal layer to its nearest neighbors in the adjacent close-packedlayers. However, atoms do not align by the nearest neighbor distancecontinuously along this direction, but align alternatively with shortand very long spacings as show in FIG. 1. The second near-neighbordirection in Ti is <11-20> which is also a close-pack direction with anequal atomic spacing. Therefore, it can be concluded that the <20-23 >and <11-20 > are the preferred directions of emission for Ti duringsputtering.

The highest step coverage and collimation efficiency is expected tooccur for polycrystalline targets having textures with high proportionsof <20-23 > and/or <11-20 > orientations perpendicular to the wafersurface. Therefore, it is preferred to have a texture in one of thesetwo orientations or in both these orientations at once. This inventioninvolves high purity Ti targets with high fraction of <20-23 >perpendicular to the target plane, or high fraction of both <20-23> and<11-20 > perpendicular to the target plane.

Metals crystallize in various crystal systems and physical propertiesfor pure metals usually depend on the direction in which they aremeasured. Physical properties of titanium (and metals generally) aredescribed by tensors. Physical properties include paramagnetic anddiamagnetic susceptibility, electrical and thermal conductivity, stress,strain, thermal expansion, piezoelectricity, elasticity, thermoelectricity and optical properties. Each of these properties can becalculated. All metals therefore exhibit physical properties controlledand defined by crystallographic texture and grain size distributions andrarely are these isotropic. Titanium physical properties are allanisotropic; thus the direction effect can be significant. The elasticmodulus of titanium, for example, can vary by as much as three-fold insingle crystal, depending on the temperature and direction ofmeasurement. Metallurgical factors affecting the physical properties oftitanium include purity, texture, grain size, lattice defects of varioussorts and the distributions and uniformities of same. Physicalproperties depend expressly on and are entirely controlled by, themetallurgical characteristics described herein.

The various slip and twinning systems can be expressed as vectors thatinvolve a direction and displacement. Each mode of deformation has acritical stress that depends on temperature and direction ofmeasurement. Therefore, mechanical properties are also controlled anddefined by the metallurgical condition of titanium. Flow stress,ductility and fracture toughness, and how each is affected by thetemperature of measurement, are examples of mechanical properties.Physical transport properties such as inter diffusion of matrix andimpurities are governed by the respective ease of atomic jumps invarious lattice directions and not all jump directions are equally easyand they are always associated with a specific vector. Grain size andtexture are important since they combine to form a distribution of grainboundary mismatch contributing more or less significantly to “pipediffusion” for example. These properties also depend expressly on themetallurgical condition.

The present invention contemplates titanium targets with tailoredtextures that provide better step coverage or higher yield (efficiency)of mechanical collimation and methods for manufacturing these targets.Better step coverage and higher collimation yield (efficiency) areachieved through increased proportion of atom emission perpendicularfrom the target surfaces during sputtering. Such controlled emissionprovides better step coverage and collimation efficiency and results ina computer chip having improved step coverage on the contact and viaholes, regardless of the hole aspect ratio.

The texture requirement for the titanium target capable of a highproportion of Ti emissions perpendicular to the target surface is basedon intensities for (hkil) crystal planes that are parallel to the targetplane, which will be referred to as intensity of (hkil) hereinafter. Anintensity, for a crystal plane is proportional to the volume fraction ofall the grains that are orientated with this crystal plane parallel tothe target plane. A value of intensity for (hkil) plane in a Ti targetis expressed as multiples (times random) of the corresponding intensityin a Ti sample with a random grain orientation distribution, and isobtained from orientation distribution function based on four measuredpole figures from X-ray diffraction:

dV/V=I(θ,Φ)dy, in which I(θ,Φ)=1/(8π²)∫f(ω,θ, Φ)dω, and dy=sin θdθdΦ

where ω,θ, and Φ are Euler angles according to FIG. 5; I(θ,Φ) is theintensity for (hkil) plane parallel to the target plane; dV is thevolume element corresponding to the orientation element dy for theentire sample; V is the total volume of the sample; “∫” representsintegration from 0° to 360° with respect to ω; and f(ω,θ,Φ) is theorientation distribution function constructed from experimental polefigures. The ND, RD, and TD in FIG. 5 are axes of the coordinate systemattached to the sample (sample coordinate system), and represent normaldirection (perpendicular to the target plane), rolling direction, andtransverse direction of the target, respectively. The x′, y′, and z′ areaxes of the coordinate system attached to the crystal (crystalcoordinate system) with z′ along [0002] direction which is the pole of(0002) plane. The Euler angles (ω,θ, and Φ are defined by the followingoperations. The crystal coordinate system initially coincides with thesample coordinate system, that is, x′, y′, and z′ coincide with RD, TDand ND, respectively. The crystal coordinate system is then firstrotated about the z′-axis through the angle ω, then about x′-axis (inits new orientation) through θ and finally, once again about the z′-axis(in its new orientation) through the angle Φ.

An intensity value in terms of times random for (hkil) can be understoodas a calculated X-Ray diffraction intensity from the (hkil) parallel tothe target plane scaled to that of a random sample. Since a pole of acrystal plane is perpendicular to this crystal plane, an intensity for(hkil) plane parallel to the target plane can also be considered as thepole intensity of (hkil) perpendicular to the target plane. For example,<20-23> and <11-20> are the poles of (20-25) and (11-20) planes.Therefore, the intensities of (20-25) and (11-20) also representintensities of <20-23> and <11-20>, respectively. Unlike plane anddirection indices (Miller) in cubic crystals, planes and directions inhexagonal crystals do not always share the same indices(Miller-Bravais). Only for basal or prism planes, do Miller Bravaisdirection and plane indices coincide numerically. The <20-23> and<11-20> orientations are perpendicular to the target plane when thecrystal plane (20-25) and (11-20) are parallel to the target plane,respectively (FIG. 6). Therefore, textures with <20-23> and <11-20>perpendicular to the target surface are referred hereinafter as (20-25)texture in FIG. 6A and (11-20) texture in FIG. 6B, respectively. Becausesome crystal planes such as (20-25) do not have or have extremely weakX-Ray diffraction peaks, the intensities of crystal planes arecalculated from orientation distribution function constructed from fourmeasured pole figures for (0002), (10-11), (10-13), and (11-20) ratherthan measured directly in the X-ray diffraction. A strong (20-25)texture corresponds to (0002)-36° texture (average peak intensity beingat 36° from the center of (0002) pole figure).

The expression (0002)-α represents a texture such that (0002) planeshave an average tilt angle of α relative to the target plane to besputtered. It is calculated by averaging the tilt angles of highest fiveintensity peaks on a (0002) pole figure according to the followingequation:

α=ΣI _(i)α_(i) /ΣI _(i;)

where α_(i) and I_(i) are the (0002) tilt angle relative to the targetplane for ith intensity peak and the corresponding X-Ray intensity,respectively.

The following discussion explains the correlation between thecrystallographic textures and sputter performance including stepcoverage.

In order to obtain a high proportion of Ti emission directionsperpendicular to the target surface, high proportions of grains shouldbe oriented with (20-25) and/or (11-20) planes parallel to the targetsurface as shown in FIGS. 6A and 6B. According to this invention, thefollowing crystallographic texture is preferred. The intensity of(11-20) parallel to the target plane is preferably greater than 0.4times random and the intensity of (20-25) plane parallel to the targetplane is at least 1.5 times random. In order to maximize (20-25)intensity, an average tilt angle of (0002) with respect to the targetsurface plane, is preferably between about 32° and 40°. The mostdesirable a value is about 36°. The (20-25) is sandwiched between(10-12) and (10-13) (FIG. 7). Since (20-25) is only approximately fivedegrees from these two crystal planes, high intensity of (10-12) and(10-13) should also be helpful in step coverage improvement. Thisrequires high summation of intensities for (20-25), (10-12), and(10-13). Since (0002) is as far as 36 degrees from (20-25) and 90degrees from (11-20), Ti emission is significantly away from thedirection perpendicular to the target plane for strong (0002) texture.It is therefore desirable to have very low intensity of (0002) parallelto the target plane. This invention provides targets in which theintensity of (0002) parallel to the target plane is 1.8 times random orless, and preferably less than 1.0 times random.

Two types of microstructure may be produced in the targets of thisinvention, and the texture obtained is dependent on the microstructure.The first type of microstructure contains uniformly distributed twins.The fraction of twins is defined by the area fraction of grains thatcontain twins in a cross-section of a sample. The fraction of twins canbe controlled and up to 100% twins is obtainable. The second type ofmicrostructure contains recrystallized grains. FIGS. 8A and 8Billustrate grain and twins diagrammatically and FIGS. 9A and 9B arephotomicrographs showing twins and grains, respectively. Higherintensity of (11-20) parallel to the target plane is achievable with thetwinning microstructure than with the crystallized microstructure.Greater than 1.5 times random for (11-20) parallel to the target planecan be obtained with the twinning microstructure. On the other hand, therecrystallized microstructure is associated with higher totalintensities for (20-25), (10-12), and (10-13) parallel to the targetplane. The intensity of (20-25) parallel to the target plane may begreater than three times random for the recrystallized microstructure.Also lower intensity of (0002) parallel to the target plane isachievable with the crystallized microstructure than with the twinningmicrostructure. As low as 0.3 times random for (0002) parallel to thetarget plane is achievable with the recrystallized microstructure. Grainsize as small as 10 μm is attainable and grain size as small as 5 μm isdesirable.

The targets of the invention are distinguished from conventional targetsin that (a) the targets in this invention have high intensity in thevicinity of (0002)-α (α=30°˜40° which contain strong (20-25)) and(11-20); (b) texture component of (0002) is much reduced; (c) uniformlydistributed twins in microstructure associated with high (11-20) texturecomponent; and (d) the targets provide better step coverage orcollimation yield than the conventional targets.

Since texture produced by conventional mechanical deformation, e.g.rolling and forging, spreads from (10-17) to (10-13) which is close to(20-25) texture but far away from (11-20) texture, processing methodsother than conventional methods shown in FIG. 10 must be used. Theprocessing method for forming the desired textures is described asfollows, but it should be understood that other procedures for workingTi may be used to effect the same goal. For example, different types offorging, rolling, and other metal working processes may be used withequal effect, providing metal working sequences are used that activatedeformation in the work piece to become a target in ways that takeadvantage of the slip and twinning components of deformation. Theinvention contemplates using standard metal working but in a new processto attain these desirable textures.

One such method used to obtain a texture of this invention involvesproducing the finished texture by arranging the deformation schedulewith twinning as the dominant deformation mechanism during finishingdeformation steps as opposed to slip being the dominant deformationmechanism as in conventionally processed Ti target. Significant grainrotation can be obtained through twinning with small amounts ofdeformation. FIGS. 10 and 11 compare conventional processing and theprocessing to produce oriented targets to maximize step coverageaccording to the invention. The flow chart in FIG. 11 illustrates oneprocess but it may be also possible to obtain desired orientation byother processes. As used here the term “deformation” refers to aprocedure that results in a reduction in cross sectional area orreduction in thickness.

The first processing step of this method includes a mechanicaldeformation and annealing for recrystallization. Much of the mechanicaldeformation is achieved in the first processing step, (“primarydeformation”). However, the deformation process in this step should beperformed in the alpha phase field at any temperature. A colddeformation, especially cold rolling, is preferred for better uniformityand a sharper texture. In the primary, or first, deformation a highpurity titanium billet receives a thickness reduction of more than 50%preferably more than 70%. The deformed blanks are then heat treated toobtain a recrystallized microstructure with a strong (0002)-α₁ texture.The subscript “1” denotes the result after first process step. The tiltangle α₁ is dependent on the metal working process and heat treatment.It is usually 20˜34°, and typically 30°, when the target blank is rolledmore than 70%.

In the second processing step of the method in this invention, theblanks are subsequently deformed again, such as by rolling or forging,with a thickness reduction between about 5% and 30%, preferably betweenabout 10% and 20%. This second deformation step results in a texturewith two main components, (0002)-α₂ and (11-20); the subscript 2 refersto the tilt angle α₂ observed after the second deformation. The tiltangle α₂ is usually two to six degrees higher than α₁ depending on theamount of second deformation and temperature. The difference between α₂and α₁ increases with decrease of the temperature of the seconddeformation and increase in the amount of second deformation. It ispreferred that the second deformation step be performed cryogenicallyalthough deformation at ambient temperature is acceptable.

A cryogenic rolling followed by hot rolling below recrystallizationtemperature can generate higher intensity of (11-20) parallel to thetarget plane after recrystallization than cryogenic rolling alone. Thetotal thickness reduction (in reference to the thickness at start of thecryogenic rolling) is preferably less than 35%.

A target manufactured by this method can have as-deformed or recoveredtwinning, or partially recrystallized microstructure with reducedfraction of twins, or fully recrystallized microstructure without twins.Recrystallization does not change the as-deformed tilt angle, α₂significantly. As a result of recrystallization, fraction of grains withorientations around (0002)-α₂ is increased but the fraction of (11-20)parallel to the target plane is decreased. Also, an extremely lowfraction of (0002) parallel to the target plane is obtained, which ispreferred. Target texture after a recovery heat treatment remainsessentially the same as the starting texture with twinningmicrostructure. The grains with twinning microstructure may be definedby twin boundaries which are grain boundaries of special orientations. Agrain size below 20 microns is preferred after the heat treatment in thefirst process step if the twin microstructure remains as themicrostructure in the final product. This will generate lower fractionsof (0002) parallel to the target surface, which is desired for betterstep coverage.

The primary deformation process (i.e. first deformation step) in thisinvention is used to obtain an uniform and small grain size, and toobtain the majority of total thickness reduction required. The primarydeformation, after forging an ingot to a billet, can be rolling and/orupset forging but is not limited to these methods. The target blankshould be recrystallized after the first deformation process for themaximum amount of twinning during the second deformation. The secondarydeformation, i.e. the second deformation, is used to create significantamount of (11-20) and to change α angle through twinning. The method ofdeformation can be rolling and/or forging, or any method that generatesequivalent effect in twinning and rotating grains toward (11-20). Thedeformation should be between about 5% and 30%, preferably between about10% and 20% so that twinning instead of slip is the dominant deformationmechanism. When the second deformation is below about 5%, the amount ofdeformation is too small to cause significant change in texture. Whenthe second deformation is more than about 30%, a higher fraction (0002)parallel to the target plane is obtained. The amount of twinning and(11-20) should be maximized in the second deformation by different waysincluding low deformation temperature such as cryogenic deformation,higher deformation rate, and larger grain size. Cryogenic deformation ispreferred in the second deformation although deformation under ambienttemperature can also generate significant twinning. Twinning is moredominant at cryogenic temperatures than at ambient temperature. Thecryogenic deformation also provides a more uniform twin microstructurethan deformation at ambient temperatures. Before the cryogenicdeformation, a Ti blank may be chilled to a temperature as low asconvenient or desired. Titanium is quite ductile at cryogenictemperatures, especially when it is high purity. The preferred methodsof deformation are rolling, forging or other processes that produce thesimilar result. A grain size of smaller than 20 micron after the firstprocess (combination of first deformation and heat treatment) isdesirable for lowest intensity of (0002) after the second deformation. Asmaller grain size after the first process will also result in a smallergrain size in the final product which is desired for good filmuniformity.

Preferably, a strong (0002)-α₁ texture with a, between 30 and 40 degreesshould be obtained after the first process (combination of deformationand heat treatment) so that a texture containing (0002)-α₂ in thevicinity of (0002)-36° and significant fraction of (11-20) is obtainedafter the second deformation. Ideally, more than 70% rolling reductionin the first processing step is applied so that a cryogenic deformationsuch as rolling or forging in the second deformation generates a texturewith both strong (0002)-36° and (11-20) compositions.

The minimum grain size after recrystallization of the twins is usuallylarger than the grain size before twinning. Therefore, various grainsize can be obtained by controlling both process steps. A grain sizeabove 15 μm can be obtained in the final product after the dual processor a finer grain size may be obtained if desired for good thin filmuniformity. The most effective way of reducing grain size is refininggrain size in the first deformation step. A grain size of 5 μm orsmaller is achievable through severe deformation prior to the firstdeformation (on an ingot) and on the billet in the first deformationstep, such that a grain size between 5 and 15 μm can be obtained in thefinal product. A grain size smaller than 5 μm is achievable in thetarget with the new texture if the grain size is less than about 2 μmafter the primary deformation and heat treatment.

The rolling method used in the primary and second deformations can beeither unidirectional or cross rolling. In unidirectional rolling, therolling passes are along the same direction. In cross rolling, therolling passes are along different directions. Ideally, cross rolling isperformed in rolling-pass-pairs and a rolling pass in each pair isfollowed by a second pass at 90 degrees such that the original shape oroutline is restored.

The following example, summarized in Table 1, compares the describedprocessing represented by samples No. 1 and 2 with processing examplesNo. 3 through 6 in accordance with the invention. Table 2 summarizespurities, grain size and texture of these samples. The values associatedwith crystal planes in Table 2 are intensities in terms of times random.The tilt angle of (0002) is averaged angle between (0002) plane and thetarget plane calculated by averaging five highest intensity peaks on(0002) pole figures.

The processes described below started from a cylindrical billet whichwas forged from a cylindrical cast ingot at 815° C. for 70% deformationalong the radial directions.

The composition of the samples used in the examples are described inTables 3, 4, 5 and 6. Tables 3 and 4 indicate the chemistry of ingotsfrom which Sample No. 1 and sample No. 2, respectively, were derived.Table 5 indicates the chemistry ingot from which Samples 3 and 4 weretaken and Table 6 describes the chemistry of an ingot from which Samples5 and 6 were derived. The GDMS analysis method was used to determineconcentration of all elements other than S, H, C, N and O, which wereanalyzed by the LECO method.

Sample No.1: A section of billet was cold worked to 80% deformation bycross rolling in directions 45° apart, and then annealed at 760° C. for75 minutes. The dominant texture in this sample is (0002)-11° which hashigh intensities at (0002) and (10-17). There is negligible intensity of(11-20)

Sample No.2: A section of a billet was cold worked to 80% deformation bycross rolling in directions 45° apart, and then annealed at 510° C. for120 minutes. The strongest texture component in this sample is (10-13)accompanied by higher intensity of (20-25) and lower intensity of (0002)than sample No. 1. There is negligible intensity of (11-20) in thistarget as for sample No. 1.

Sample No.3: A section of billet was cold worked to 80% deformation bycross rolling in directions 45° apart, and was then recrystallized at565° C. for 30 minutes. It was subsequently processed by cryogeniccross-rolling comprising two perpendicular passes at −73° C., withfurther 15% reduction in thickness (in reference to the finishingthickness of the cold rolling). The cryogenically rolled sample was heattreated at 427° C. for 30 minutes, which brought about recovery only.The heat-treated sample has significant intensity peaks at both (11-20)and (20-25), and contains more than 95% twins. This process alsogenerated weaker (0002) intensity.

Sample No.4: A section of billet was cold worked to 80% deformation bycross rolling in directions 45° apart, and was then recrystallized at621° C. for 30 minutes. It was subsequently processed by cryogeniccross-rolling comprising two perpendicular passes at −73° C., withfurther 15% reduction (in reference to the finishing thickness of thecold rolling). The cryogenically rolled sample was heat treated at 635°C. for 60 minutes, which brought about recrystallization. Theheat-treated sample has a stronger intensity of (20-25) than sampleNo.3. It also has much reduced intensity of (0002) compared to samplesNo.1 through No.3. There a lower intensity of (11-20) in this targetthan in sample No. 3 due to recrystallization.

Sample No.5 A section of billet was cold worked to 75% deformation bycross rolling in directions 45° apart, and was then recrystallized at593° C. for 45 minutes. It was subsequently processed by cryogeniccross-rolling comprising two perpendicular passes at −48° C., withfurther 14% reduction (in reference to the finishing thickness of thecold rolling). The cryogenically rolled sample was heat treated at 704°C. for 60 minutes, which brought about recrystallization. This targethas intermediate intensity of (11-20), relatively strong intensity of(20-25) among the targets.

Sample No.6 A section of billet was cold worked to 75% deformation bycross rolling in directions 45° apart, and was then recrystallized at565° C. for 45 minutes. The second deformation step included a cryogeniccross-rolling followed by a hot cross-rolling reduction. The cryogenicrolling comprised two perpendicular passes at −73° C., with 14%reduction (in reference to the finishing thickness of the cold rolling).The cryogenically rolled blank was subsequently soaked in a furnace at510° C. for 30 minutes before the hot rolling, which did not result insignificant recyrstallization. The hot rolling comprised twoperpendicular passes at 310° C., with 12.6% reduction (in reference tothe finishing thickness of the cold rolling), which brought about a26.6% total amount of second deformation. The blank was then heattreated at 593° C. for 60 minutes for recrystallization. This target hasa relatively high intensity of (11-20), but lower intensity of (20-25).

Table 2 also show the titanium purity of the samples: “5N5” indicates99.9995 wt. % Ti; “5N8” indicates 99.9998 wt. % Ti; and “5N” indicates99.999 wt. % Ti; all percentages exclude gases.

TABLE 1 Summary of Processes for Targets in Example Two Example ProcessNo. 1 A section of billet → Cold cross-rolling 80% → Annealing at 760°C. for 75 minutes. No. 2 A section of billet → Cold cross-rolling 80% →Annealing at 510° C. for 120 minutes. No. 3 A section of billet →Primary deformation: cold cross-rolling 80% → Annealing at 565° C. for30 minutes → Second deformation: cryogenic cross-rolling 15% at −73° C.→ Recovery annealing at 427° C. for 30 minutes. No. 4 A section ofbillet → Primary deformation: cold cross-rolling 80% → Annealing at 621°C. for 30 minutes → Second deformation: cryogenic cross-rolling 15% at−73° C. Recrystallization annealing at 635° C. for 60 minutes. No. 5 Asection of billet → Primary deformation: cold cross-rolling 75% →Annealing at 593° C. for 45 minutes → Second deformation: cryogeniccross-rolling 14% at −48° C. → Recrystallization annealing at 704° C.for 60 minutes. No. 6 A section of billet → Primary deformation: coldcross-rolling 75% → Annealing at 565° C. for 45 minutes → Seconddeformation: cryogenic cross-rolling 14% at −73° C. → heat treatment at510° C. for 30 minutes → cross-rolling 12.6% at 310° C. (total seconddeformation of 26.6%) Recrystallization annealing at 593° C. for 60minutes.

TABLE 2 Purity, Grain Size and Texture (times random) No. 1 No. 2 No. 3No. 4 No. 5 No. 6 Metallic 5N5 5N8 5N 5N 5N 5N Purity Grain Size 75  14   <10 *  29   73   26   (μm) (0002) tilt 11°  34°  37°  37°  28° 30°  angle (10-10) 0.0 0.0 0.0 0.6 0.2 0.4 (0002) 5.5 2.5 1.3 0.4 0.41.3 (10-11) 0.0 0.0 0.0 0.0 0.2 0.0 (10-12) 1.4 1.2 1.6 2.3 1.8 1.0(10-13) 2.7 6.2 2.2 2.9 3.0 2.6 (10-15) 7.3 5.5 2.3 1.1 2.9 3.8 (10-17)10.0  5.5 1.8 0.8 1.3 2.3 (11-20) 0.0 0.1 1.8 1.4 0.6 0.9 (20-25) 2.33.2 2.5 3.5 3.3 2.6 * Twins in 95% area of grains.

TABLE 3 Ele- Concentration Ele- Concentration Ele- Concentration ment(ppm wt.) ment (ppm wt.) ment (ppm wt.) Li <0.005 Ga <0.050 La <0.005 Be<0.005 Ge <0.050 Ce <0.005 B <0.010 As <0.010 Nd <0.005 F <0.050 Se<0.010 Hf <0.050 Na 0.020 Br <0.010 Ta <1.000 Mg <0.010 Rb <5.000 W<0.010 Al 0.230 Sr <3000 Re <0.010 Si 0.130 Y <200 Os <0.010 P <0.010 Zr0.540 Ir <0.010 S 6.000 Nb <0.200 Pt <0.050 Cl 0.030 Mo <0.050 Au <0.050K <0.010 Ru <0.010 Hg 0.100 Ca <0.200 Rh <0.010 Tl <0.010 Sc <0.050 Pd<0.010 Pb <0.010 Ti matrix Ag <0.050 Bi <0.010 V 1.600 Cd <0.050 Th<0.0005 Cr 0.130 In <0.050 U <0.0005 Mn <0.005 Sn <0.050 H 3.050 Fe2.000 Sb <0.050 C 7.000 Co <0.005 Te <0.050 N 3.000 Ni 0.010 I <0.010 O70 Cu <0.050 Cs <0.010 Zn <0.100 Ba <0.005

TABLE 4 Ele- Concentration Ele- Concentration Ele- Concentration ment(ppm wt.) ment (ppm wt.) ment (ppm wt.) Li <0.005 Ga <0.050 La <0.005 Be<0.005 Ge <0.050 Ce <0.005 B <0.010 As <0.010 Nd <0.005 F <0.050 Se<0.050 Hf <0.010 Na <0.010 Br <0.050 Ta <5.000 Mg <0.050 Rb <5.000 W<0.010 Al 0.100 Sr <3000 Re <0.010 Si 0.100 Y <200 Os <0.010 P <0.010 Zr<0.480 Ir <0.010 S 1.000 Nb <0.200 Pt <0.050 Cl <0.010 Mo <0.050 Au<0.050 K <0.010 Ru <0.010 Hg <0.010 Ca 0.400 Rh <0.050 Tl 0.100 Sc<0.050 Pd <0.010 Pb <0.010 Ti matrix Ag <0.050 Bi <0.020 V 0.550 Cd<0.050 Th <0.0005 Cr 0.068 In <0.050 U <0.0005 Mn <0.005 Sn <0.050 H1.000 Fe 2.100 Sb <0.050 C 5.000 Co 0.007 Te <0.050 N 2.000 Ni 0.055 I<0.010 O 79 Cu <0.050 Cs <0.010 Zn <0.050 Ba <0.005

TABLE 5 Ele- Concentration Ele- Concentration Ele- Concentration ment(ppm wt.) ment (ppm wt.) ment (ppm wt.) Li <0.005 Ga <0.050 La <0.005 Be<0.005 Ge <0.050 Ce <0.005 B <0.010 As <0.010 Nd <0.005 F <0.050 Se<0.050 Hf <0.010 Na 0.010 Br <0.050 Ta <5.000 Mg <0.050 Rb <5.000 W<0.010 Al 0.200 Sr <3000 Re <0.010 Si 0.230 Y <200 Os <0.010 P <0.010 Zr0.370 Ir <0.010 S 4.000 Nb <0.200 Pt <0.050 Cl 0.005 Mo <0.050 Au <0.050K <0.010 Ru <0.010 Hg 0.100 Ca <0.500 Rh <0.050 Tl <0.010 Sc <0.050 Pd<0.010 Pb <0.010 Ti matrix Ag <0.050 Bi <0.020 V 0.660 Cd <0.050 Th<0.0005 Cr 0.070 In <0.050 U <0.0005 Mn <0.005 Sn <0.050 H 2.000 Fe8.800 Sb <0.050 C 19.000 Co <0.010 Te <0.050 N 2.000 Ni 0.010 I <0.010 O228 Cu <0.050 Cs <0.010 Zn <0.050 Ba <0.005

TABLE 6 Ele- Concentration Ele- Concentration Ele- Concentration ment(ppm wt.) ment (ppm wt.) ment (ppm wt.) Li <0.005 Ge <0.050 Nd <0.005 Be<0.005 As <0.010 Sm <0.005 B <0.010 Se <0.050 Eu <0.005 F <0.050 Br<0.050 Gd <0.005 Na 0.010 Rb <5.000 Tb <0.005 Mg <0.050 Sr <3000 Dy<0.005 Al 1.300 Y <200 Ho <0.005 Si 0.380 Zr 0.420 Er <0.005 P <0.010 Nb<0.200 Tm <0.005 S 0.700 Mo <0.050 Yb <0.005 Cl 0.01 Ru <0.010 Lu <0.005K <0.010 Rh <0.050 Hf <0.010 Ca 0.400 Pd <0.010 Ta 5000 Sc <0.050 Ag<0.050 W <0.010 Ti matrix Cd <0.050 Re <0.010 V 0.190 In <0.050 Os<0.010 Cr 0.180 Sn <0.050 Ir <0.010 Mn <0.005 Sb <0.050 Pt <0.050 Fe3.800 Te <0.050 Au <0.050 Co 0.005 I <0.010 Hg <0.100 Ni 0.030 Cs <0.010Tl <0.010 Cu 0.170 Ba <0.005 Pb <0.010 Zn <0.050 La <0.005 Bi <0.020 Ga<0.050 Ce <0.005 Th <0.0005 Pr <0.005 U <0.0005

As shown in Table 7, target No. 1 which has strongest (0002) intensityhas lowest step coverage. Target No. 2 provide slightly higher stepcoverage than target No. 1. Since both target No. 1 and No. 2 havenegligible (11-20) intensity, the slightly improved step coverageassociated with target No.2 should be a result of reduced (0002) andincreased intensity in the vicinity of (20-25). Further step coverageimprovement can be achieved by increasing intensity of (11-20) andfurther decreasing intensity of (0002) as shown by targets No. 3 throughNo. 6. Statistical analysis showed that the differences in step coverageare indeed from texture effects. It should be noted, however, that stepcoverage is dependent on sputter system and configuration of sputtering.Therefore, greater or smaller step coverage improvement may occur on adifferent sputter system or different configuration of sputtering.

TABLE 7 Sputtering Performance Aspect Ratio No. 1 No. 2 No. 3 No. 4 No.5 No. 6 1.00 0.235 0.240 0.255 0.256 0.251 0.259 1.39 0.152 0.159 0.1680.164 0.163 0.168 1.78 0.105 0.108 0.114 0.116 0.111 0.111 2.21 0.0730.076 0.081 0.078 0.079 0.082 2.56 0.058 0.060 0.065 0.062 0.064 0.068Mean Step 0.125 0.129 0.137 0.135 0.134 0.138 Coverage

It is apparent from the foregoing that various changes and modificationsmay be made without departing from the invention. Accordingly, theinvention should be limited only by the appended claims.

What is claimed is:
 1. A method of making a titanium sputtering targetcomprising providing a titanium billet, deforming the billet,recrystallizing the microstructure and changing the texture primarilythrough twinning during a second deformation of the recrystallizedmicrostructure.
 2. A method according to claim 1 comprising deformingthe billet by 50% or more, followed by an annealing forrecrystallization, followed by a second deformation of from about 5% toabout 30% such that twinning is a primary deformation mode with orwithout an annealing after the second deformation.
 3. A method accordingto claim 2 wherein deformation is by rolling and/or forging.
 4. A methodaccording to claim 2 further comprising deforming the billet at ambienttemperature or lower in the second deformation step.
 5. A methodaccording to claim 2 wherein the second deformation is at a temperatureof less than or equal to about −48° C.
 6. A method according to claim 2wherein at least one of the first and second deformations comprises oneor both of unidirectional rolling and cross rolling.
 7. A method ofprocessing titanium to produce a sputtering target comprising:mechanically deforming a high purity titanium billet in the alpha phaseto a thickness reduction greater than about 50%; heat treating thedeformed billet to obtain a recrystallized microstructure within thetitanium and having a (0002)-α₁ plane texture; deforming the heattreated titanium to a thickness reduction of from about 5% to about 30%at a temperature of less than or equal to about −48° C. to alter themicrostructure texture of the titanium and produce planes (0002)-α₂within the texture; and after deforming the heat treated titanium,producing one of the following in the microstructure of the titanium:(1) as-deformed or recovered twins obtained by additional heattreatment; (2) partially recrystallized microstructure with reducedfraction of twins obtained by additional heat treatment; or (3) fullyrecrystallized microstructure without twins obtained by additional heattreatment.
 8. A method according to claim 7 wherein the mechanicaldeformation of titanium billet is to a thickness reduction greater thanabout 70%.
 9. A method according to claim 7 wherein the tilt angle α₂ isabout 32° to 40°.
 10. A method according to claim 7 wherein the seconddeformation of the heat treated titanium is between about 10% to 20%.11. A method according to claim 7 wherein the tilt angle α₂ after thesecond deformation is about 2° to 6° higher than the tilt angle of α₁after the first deformation.
 12. A method according to claim 11 whereinthe tilt angle α₁ is about 31° and tilt angle α₂ is about 36°.
 13. Amethod according to claim 11 wherein the deformation of the heat treatedtitanium is performed at ambient temperature or below.
 14. A methodaccording to claim 11 wherein the heat treated titanium is deformed toproduce a microstructure wherein twins are produced from grains with agrain size below about 20 microns.
 15. A method according to claim 11wherein the second deformation is followed by another deformation belowthe recrystallization temperature of the titanium.